Getting Facebook working on a SIM means using the SIM Toolkit commands, which limits interaction to a cascade of text menus, but it does mean that any GSM handset can now access Facebook. Handsets don’t even need an internet connection as the service uses Class 2 SMS for connectivity (SMS messages sent and received by the SIM without user interaction)
Totally makes sense for countries where Facebook didn’t take of yet and where users don’t want to (or can’t) spend money on smartphones and/or data subscriptions.